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Questions People Ask About Cancer

There are a lot of rumors and myths about cancer that make it hard for people to know what’s true about this disease. Here we address some of the common questions people ask about cancer. If you want to know more about how cancer starts and spreads, please see What Is Cancer? If you have questions that aren’t answered here, please call one of our Cancer Information Specialists any time, day or night, at 1-800-227-2345 or visit us online at www.cancer.org.

How common is cancer?

About half of all men and one-third of all women in the US will develop cancer during their lifetimes.

The risk of developing most types of cancer can be reduced by changes in a person’s lifestyle, for instance, by staying away from tobacco, limiting time in the sun, and being physically active and eating healthy foods.

There are also screening tests that can be done for some types of cancers so they can be found as early as possible – while they are small and before they have spread. In general, the earlier a cancer is found and treated, the better the chances are for living for many years.

Who gets cancer?

Over one and a half million new cancer cases are diagnosed each year. Anyone can get cancer at any age, but the risk goes up with age. About 78% of all cancers are diagnosed in people age of 55 and older. Cancer can be found in Americans of all racial and ethnic groups, but the rate of cancer occurrence (called the incidence rate) varies from group to group.

How many people alive today have ever had cancer?

Today, nearly 14.5 million people alive in the United States have had some type of cancer. Some of these people are cancer-free; others still have it.

Years ago, most people who had cancer did not live very long. That’s not the case anymore. Every year more and more people survive cancer. This is especially true of children with cancer and those whose cancers were found early, before they spread.

The survival rates are different for people with different types of cancers. Some types of cancer grow very slowly. Some respond to treatment very well. Others grow and spread faster and are harder to treat. If you know someone who has cancer, keep in mind that what happens to them could be very different from what happens to someone else with another type of cancer.

What causes cancer?

Things people do

Some cancers are caused by things people do or expose themselves to. For example, tobacco use can cause cancer of the lungs, mouth, throat, bladder, kidneys, and many other organs. Of course, not everyone who uses tobacco will get cancer, but it greatly increases a person’s risk. It increases their chance of developing heart and blood vessel disease, too.

Spending a lot of time in the sun without protection can cause skin cancer. Melanoma is a very serious form of skin cancer linked to sunlight and tanning bed exposure.

Other things people are exposed to

Radiation can cause cancer. For instance, people exposed to nuclear fallout have a higher cancer risk than those who were not exposed. Rarely, radiation treatment for one type of cancer can cause another cancer to grow many years later. This is why doctors and dentists use the lowest possible doses of radiation for x-rays and scans (much lower than the doses used for cancer treatment).

Certain chemicals have been linked to cancer, too. Being exposed to or working with them can increase a person’s risk of cancer. Call us to learn more about the carcinogens (substances that cause cancer) that may be around you, or see the “Other Carcinogens” section of our website.

Genes that run in families

About 5% to 10% of all cancers are linked to genes that are inherited from parents.

Bottom line

No one knows the exact cause of most cases of cancer. We know that certain changes in our cells can cause cancer to start, but we don’t yet know exactly how it all happens. Scientists are studying this problem and learning more about the many steps it takes for cancers to form and grow. See the “What Causes Cancer?” section of our website to learn more about the things that have been linked to this disease.

If you are interested in taking measures to help reduce your cancer risk, see the section below called “Can cancer be prevented?”

Can injuries cause cancer?

It’s a common myth that injuries can cause cancer. But the fact is that falls, bruises, broken bones, or other such injuries have not been linked to cancer. Sometimes a person might visit the doctor for what’s thought to be an injury and cancer is found at that time. But the injury did not cause the cancer; the cancer was already there. It also sometimes happens that a person will remember an injury that happened long ago in the place cancer was found.

Rarely, burn scars can be the site of cancer many years after the burn has healed. Most often, skin cancer is the type that starts in a burn scar.

Can stress cause cancer?

Researchers have done many studies to see if there’s a link between personality, stress, and cancer. No scientific evidence has shown that a person’s personality or outlook affects their cancer risk.

There are many factors to look at in the relationship between stress and cancer. It’s known that stress affects the immune system, but so do many other things. Despite many studies, a link between psychological stress and cancer has not been proven. Looking at the studies that have been done, it seems they sometimes come to opposite conclusions.

For instance, in one large Danish study, people who reported major stressors in their lives did not appear to have a seriously increased risk for any type of cancer. Another study that looked at women with major life stressors, such as divorce or the death of someone close, found a slight increase (about 1/3 higher than average) in breast cancer compared to women without these stressors. In the area of day-to-day stress, another study showed higher breast cancer risk linked to stress. Yet another found that women reporting higher day-to-day stress actually were less likely to be diagnosed with breast cancer within the next 18 years.

It’s hard to explain these differences. Some may be related to the groups that were studied, while others may be due to the way the study was done. Chance may have played a role, too. All that can be said for now is that a definite link between stress and cancer risk has not been found.

What are the risk factors for cancer?

A risk factor is anything linked to your chance of getting a disease, such as cancer. Different cancers have different risk factors. For instance, exposing skin to strong sunlight is a risk factor for skin cancer, but it’s not linked to colon cancer. Some risk factors can actually cause cancer, while others may simply be more common in people who get cancer. For example, old age by itself doesn’t cause cancer, but it is a risk factor.

But risk factors don’t tell us everything. Having one risk factor, or even many, does not mean that someone will get cancer. Some people with one or more risk factors never develop the disease, while others who do develop cancer have no known risk factors. Even when a person who has a risk factor is diagnosed with cancer, there’s no way to prove that the risk factor actually caused the cancer.

There are different kinds of risk factors. Some, like a person’s age or race, can’t be changed. Others are linked to cancer-causing factors in the environment. Still others are related to personal actions, such as smoking. Some factors influence risk more than others, and a person’s risk for cancer can change over time, due to factors such as aging or lifestyle. (See the section called “What causes cancer?” for more on this.)

Some of the major cancer risk factors that can be controlled:

  • Tobacco use
  • Diet
  • Physical activity
  • Weight
  • Alcohol use
  • Sun exposure
  • Environmental exposures, such as radon, lead, and asbestos
  • Exposure to infections like hepatitis, HPV, and HIV

Overall, environmental factors, defined broadly to include tobacco use, diet, obesity, sun exposure, and infectious diseases, as well as chemicals and radiation cause an estimated 75% to 80% of all cancer cases in the United States.

Is cancer contagious?

In the past, people often stayed away from someone who had cancer. They were afraid they might “catch” the disease. But cancer isn’t like the flu or a cold. You can’t catch cancer from someone who has it. You won’t get cancer by being around or touching someone with cancer. Don’t be afraid to visit someone with cancer. They need the support of their family and friends.

You can get more details on this in Is Cancer Contagious?

Can cancer be prevented?

There’s no sure way to prevent cancer, but there are things you can do to help reduce your chances of getting it.


Many cancers might be prevented if people didn’t use tobacco.

Smoking damages nearly every organ in the human body and accounts for some 30% of all cancer deaths. Cigarettes, cigars, pipes, and oral (smokeless) tobacco products cause cancer and should not be used. People who use tobacco should try to quit. Studies clearly show that ex-smokers have less cancer than people who continue to smoke.

It’s best to never use tobacco at all and to stay away from secondhand smoke.

See the “Stay Away from Tobacco” section of our website for more on this.


Drinking alcohol is linked to a higher risk of certain types of cancer.

Some people think that certain types of alcohol are safer than others. But ethanol is the type of alcohol found in all alcoholic drinks, whether they are beers, wines, or liquors (distilled spirits). Overall, it’s the amount of alcohol that’s drunk over time, not the type of drink, which seems to be the most important factor in raising cancer risk.

If you drink, limit your intake to no more than 2 drinks per day for men and 1 drink a day for women. This may help curb your cancer risk. You can find out more in Alcohol Use and Cancer.

Drinking and smoking

The combined use of alcohol and tobacco raises the risk of mouth, throat, voice box, and esophagus cancer far more than the effects of either one alone.

Ultraviolet (UV) rays and sunlight

You can lower your chances of getting skin cancer by

  • Staying out of the sun between the hours of 10 a.m. and 4 p.m.
  • Wearing a hat, shirt, and sunglasses when you are in the sun
  • Using sunscreen with a sun protection factor (SPF) of 30 or higher
  • Not using tanning beds or sun lamps

See the “Sun and UV Exposure” section of our website to learn more about the link between UV exposure and skin cancer and to learn how to protect yourself and the people you care about from UV skin damage.


We know that our diet (what we eat or don’t eat) is linked to some types of cancer, but the exact reasons are not yet clear. The best information we have suggests a lower cancer risk for people who:

  • Eat a lot of fresh vegetables and fruits (at least 2½ cups a day)
  • Choose whole grains rather than refined grains and sugars
  • Limit red meats (beef, pork, and lamb)
  • Limit processed meats (such as bacon, deli meats, and hot dogs)
  • Choose foods in amounts that help them get to and stay at a healthy weight
  • Limit alcohol intake to 1 alcoholic drink a day or less for women and 2 or less for men

We have a lot of information on how diet and physical activity can affect cancer risk. Call us or visit our website to learn more.

Vaccines that help reduce cancer risk

We now know that some cancers are caused by infections, mostly viruses. One virus that’s clearly linked to cancer is the human papilloma virus (HPV). It’s been linked to cervical cancer, anal cancer, many genital cancers, and even head and neck cancers. (See HPV and Cancer for more details.)

There are vaccines to help prevent HPV infections, so they should help prevent the cancers caused by HPV. But most adults have already been infected with HPV, and the vaccines haven’t been proven to help people who already have HPV. Still, young people who are not yet sexually active should have a lower future cancer risk if they get a series of one of the vaccines before they’re exposed to HPV. The American Cancer Society recommends them for girls and boys aged 11 and 12, though they can be given as young as age 9. Vaccination is also recommended up to age 26 in women, as well as in certain males who may be at higher risk for HPV infection. To learn more, see HPV Vaccines.

Early detection

To find cancer early, while it’s small and before it has spread, adults should have regular tests called cancer screening tests. These tests help doctors find common cancers before they cause symptoms. For example, regular screening can find cancers of the breast, colon, rectum, cervix, mouth, and skin early. If cancer is found early, it can be easier to treat. Survival also tends to be longer for those with early cancer. Talk to your doctor about which screening tests might be right for you.

You can learn more about things you can do to help find cancer early in American Cancer Society Guidelines for the Early Detection of Cancer.

How is cancer diagnosed?

A person’s signs and symptoms are not enough to know whether or not cancer is present. (See Signs and Symptoms of Cancer for more on this.) If your doctor suspects cancer you will need more tests, such as x-rays, blood tests, or a biopsy. In most cases a biopsy is the only way to be sure whether cancer is present.

To do a biopsy a piece of the lump or abnormal area is taken out and sent to the lab. There, a doctor who specializes in diagnosing diseases (pathologist) looks at the cells under a microscope to see if cancer cells are present. If there are cancer cells, the doctor tries to figure out what type of cancer it is and how fast it’s likely to grow.

Scans can measure the size of the cancer and can often show if it has spread to nearby tissues. Blood tests can tell doctors about your overall health, show how well your organs are working, and give information about blood cancers.

How is cancer treated?

Surgery, chemotherapy, and radiation are the 3 main types of cancer treatment. A person with cancer may have any or all of these treatments. The cancer care team will discuss all the treatment options with the patient. It’s important to take time and think about all the options. In choosing a treatment plan, the most important factors are generally the type of cancer and the stage (amount) of the cancer. Other factors to consider include the person’s overall health, the likely side effects of the treatment, and the probability of curing the cancer, controlling it to extend life, or relieving symptoms.


Surgery is often the first treatment used if the cancer can be removed from the body. Sometimes only part of the cancer can be removed. Radiation or chemotherapy might be used to shrink the cancer before or after surgery.

For more on this, see our surgery information.


Doctors use chemotherapy or “chemo” drugs to kill cancer cells. Usually, the drugs are given intravenously (IV or into a vein) or taken by mouth. Chemo drugs travel throughout the body in the bloodstream. They can reach cancer cells that may have spread away from the tumor.

See our information on chemotherapy to learn more about chemo and its effects.

Radiation therapy

Radiation therapy is treatment with high energy rays (such as x-rays) to kill or shrink cancer cells. The radiation may come from outside the body, called external radiation, or from radioactive materials placed right into the tumor (internal or implant radiation). Getting external radiation is a lot like getting an x-ray. It’s doesn’t hurt, but it can cause side effects.

Visit our radiation therapy pages to learn more.

Other types of cancer treatment

Other kinds of treatment you might hear about include targeted therapy, stem cell or bone marrow transplant, and immunotherapy. Hormone therapy is another type of treatment that’s sometimes used to treat certain kinds of prostate and breast cancers.

What are the side effects of cancer treatment?

The type of treatment a person gets depends on the type and stage (extent) of the cancer, their age and overall health, their medical history, and their personal preferences. Each drug or treatment plan has different side effects. It’s hard to predict what side effects a person will have; even when people get the same treatment they can have different side effects. Some can be severe and others fairly mild. It’s true that some people have a tough time with cancer treatment, but many others manage quite well. And most cancer treatment side effects can be treated.

Chemo side effects

Short-term (and often treatable) side effects of chemo can include things like nausea and vomiting, appetite loss, hair loss, and mouth sores. Because chemo can damage the blood-making cells in the bone marrow, patients may have low blood cell counts. This can lead to:

  • Higher risk of infection (from a shortage of white blood cells)
  • Bleeding or bruising after minor cuts or injuries (from a shortage of blood platelets)
  • Anemia (from low red blood cell counts), which can cause tiredness, shortness of breath, pale skin, and other symptoms

(See Understanding Your Lab Test Results for more details in blood counts and what they mean.)

Cancer care teams work carefully with patients to manage the side effects of chemo. Most chemo side effects go away after treatment ends. For example, hair lost during treatment grows back after treatment is over. In the meantime, most patients are able to use wigs, scarves, or hats to cover, warm, or protect their heads.

Radiation side effects

Radiation treatments are much like x-rays and are not painful. The most common side effects are skin irritation and fatigue. Fatigue is a feeling of extreme tiredness and low energy that does not get better with rest. It often lasts for many weeks after treatment ends. Other side effects can happen, too, depending on what part of the body is being treated.

Is cancer treatment worse than cancer?

This is a belief that can be dangerous to many people. People who think treatment is worse than cancer might not get the treatments that can save their lives.

It’s easy to understand one of the sources of this belief. Often people diagnosed with early cancer have not yet had any symptoms or problems, or the problems they’ve had have been fairly small. In the early stages of cancer, symptoms tend to be minor, if there are any at all. It’s often only after the treatment begins that people start to feel sick. It’s also true that chemo, radiation, and surgery can cause side effects. But these fade after the treatment is over, and the treatment can be life-saving for many people.

A person who is thinking of refusing cancer treatment should talk with the doctor to clearly understand the likely outcomes of both treatment and non-treatment before making a decision.

If cancer is allowed to progress without treatment, symptoms get worse and new symptoms build up over time. Symptoms differ based on the type of cancer and the locations to which it spreads. Later in the course of cancer, when more serious symptoms start, curative treatment may not be an option. Cancer kills by invading key organs (like the intestines, lungs, brain, liver, and kidneys) and interfering with body functions that are necessary to live. Untreated cancer commonly causes death.

In contrast, cancer treatment often saves lives – especially when cancer is found and treated early. Even when it can’t cure the cancer, treatment can often prolong life. And medical care can always be used to help make a person more comfortable by reducing pain and other symptoms. It’s important that a person knows the goal of each course of treatment, and makes informed decisions throughout the cancer experience.

There are times when every person being treated for cancer questions their commitment to the difficult journey of treatment and its side effects. Sometimes they get discouraged by the uncertainty of treatment and wonder if it’s worth it. This is normal. It may help to know that doctors are always learning better ways to work with patients to control side effects. And remember, each year brings advances in cancer treatments, too.

What is remission?

Some people think that remission means the cancer has been cured, but this isn’t always the case. Remission is a period of time when the cancer is responding to treatment or is under control. In a complete remission, all the signs and symptoms of cancer go away and cancer cells can’t be detected by any of the tests available for that cancer. It’s also possible for a patient to have a partial remission. This is when the cancer shrinks but doesn’t completely disappear. Remissions can last anywhere from several weeks to many years. Complete remissions may go on for years and over time be considered cures. If the cancer returns (recurs), another remission may be possible with further treatment.


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Last Medical Review: 08/11/2014
Last Revised: 07/19/2016